A method of forming fine patterns includes a photolithography method, an ion beam method, a laser exposure method, and so on. The ion beam method may be used to form a fine pattern having a finer line width because the line width of an ion beam is narrow and thus used to fabricate advanced products or high-integrated semiconductors. The laser exposure method is used to form a fine pattern by coating a photosensitive film, having varying physical properties by a laser, on a substrate, radiating a laser beam on the photosensitive film, and performing an etch process.
However, the laser exposure method may be used to quickly form fine pattern, but it has a limited fine pattern width because it has a thicker line width than the ion beam method. FIG. 1 is a cross-sectional view diagrammatically showing a conventional apparatus 10 for forming fine patterns using a laser exposure method.
As shown in FIG. 1, the conventional apparatus for forming fine patterns includes a laser generator 20, a light ballast 30, a shutter 40, an exposure head 50, beam splitters 31, a tilt mirror 90, an exposure lens 110, a substrate mounting unit 130, a substrate jig 131, an X stage 120, a Y stage 150, and a rotation stage 140. The intensity of radiation of a laser beam 1, generated by the laser generator 20 and configured to have a specific wavelength, is controlled and stabilized (that is, the intensity of radiation becomes uniform) by the light ballast 30. Next, the laser beam 1 is regulated by the shutter 40 and then incident on the exposure head 50. The path of the laser beam 1 incident on the exposure head 50 is changed by the beam splitters 31 and the tilt mirror 90 and then scanned on a photosensitive film 6, coated on a top surface of a substrate 5, via the exposure lens 110.
Furthermore, the rotation stage 140 is actuated to rotate the substrate mounting unit 130 around the Z axis, the X stage 120 is actuated to move the exposure head 50 in the X-axis direction, and the Y stage 150 is actuated to move the substrate mounting unit 130 in the Y-axis direction, thereby scanning the laser beam 1 on the photosensitive film 6. After the laser beam 1 is scanned on the photosensitive film 6, a fine pattern is formed on the substrate 5 by removing the photosensitive film on which the laser beam is not scanned by using an etchant.
FIG. 2 is a top view of a computer-producing hologram lens 7 having a fine pattern formed thereon by using the conventional apparatus for forming fine patterns using a laser exposure method. Referring to FIG. 2, a fine pattern on the inner portion of a concentric circle has a line width A of 169,607.42 nm, and a fine pattern on the outer portion of the concentric circle has a line width A of 3,271.53 nm. The line width of a fine pattern, formed by the conventional apparatus for forming fine patterns by employing a laser exposure method, has a limited line width because of the diffraction limit of an exposure lens. The diffraction limit is defined to be 1.22λ/NA. Here, λ is the wavelength of a laser beam, and NA is the numerical aperture of the exposure lens (the diameter and focal distance of the exposure lens). Accordingly, there is a need for a method of further improving the line width of a fine pattern by reducing the line width of a laser beam scanned on a photosensitive film.